Re: [RFC v2 4/8] drm/fb-helper: Ensure driver module is pinned in fb_open()

[Daniel Vetter <daniel@ffwll.ch>]

On Wed, Jan 03, 2018 at 11:21:06PM +0100, Noralf Trønnes wrote:
> If struct fb_ops is defined in a library like cma, fb_open() and fbcon
> takes a ref on the library instead of the driver module. Use
> fb_ops.fb_open/fb_release to ensure that the driver module is pinned.
> 
> Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
> ---
>  drivers/gpu/drm/drm_fb_helper.c | 40 ++++++++++++++++++++++++++++++++++++++++
>  include/drm/drm_fb_helper.h     | 13 +++++++++++++
>  2 files changed, 53 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
> index 035784ddd133..2c6adf1d80c2 100644
> --- a/drivers/gpu/drm/drm_fb_helper.c
> +++ b/drivers/gpu/drm/drm_fb_helper.c
> @@ -1207,6 +1207,46 @@ void drm_fb_helper_cfb_imageblit(struct fb_info *info,
>  }
>  EXPORT_SYMBOL(drm_fb_helper_cfb_imageblit);
>  
> +/**
> + * drm_fb_helper_fb_open - implementation for &fb_ops.fb_open
> + * @info: fbdev registered by the helper
> + * @user: 1=userspace, 0=fbcon
> + *
> + * If &fb_ops is wrapped in a library, pin the driver module.
> + */
> +int drm_fb_helper_fb_open(struct fb_info *info, int user)
> +{
> +	struct drm_fb_helper *fb_helper = info->par;
> +	struct drm_device *dev = fb_helper->dev;
> +
> +	if (info->fbops->owner != dev->driver->fops->owner) {

Actually bikeshed potential here: I'd just unconditionally grab the module
reference, makes the code simpler. Or is there a reason not to?
-Daniel

> +		if (!try_module_get(dev->driver->fops->owner))
> +			return -ENODEV;
> +	}
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(drm_fb_helper_fb_open);
> +
> +/**
> + * drm_fb_helper_fb_release - implementation for &fb_ops.fb_release
> + * @info: fbdev registered by the helper
> + * @user: 1=userspace, 0=fbcon
> + *
> + * If &fb_ops is wrapped in a library, unpin the driver module.
> + */
> +int drm_fb_helper_fb_release(struct fb_info *info, int user)
> +{
> +	struct drm_fb_helper *fb_helper = info->par;
> +	struct drm_device *dev = fb_helper->dev;
> +
> +	if (info->fbops->owner != dev->driver->fops->owner)
> +		module_put(dev->driver->fops->owner);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(drm_fb_helper_fb_release);
> +
>  /**
>   * drm_fb_helper_set_suspend - wrapper around fb_set_suspend
>   * @fb_helper: driver-allocated fbdev helper, can be NULL
> diff --git a/include/drm/drm_fb_helper.h b/include/drm/drm_fb_helper.h
> index b069433e7fc1..a593f01ff69e 100644
> --- a/include/drm/drm_fb_helper.h
> +++ b/include/drm/drm_fb_helper.h
> @@ -297,6 +297,9 @@ void drm_fb_helper_cfb_copyarea(struct fb_info *info,
>  void drm_fb_helper_cfb_imageblit(struct fb_info *info,
>  				 const struct fb_image *image);
>  
> +int drm_fb_helper_fb_open(struct fb_info *info, int user);
> +int drm_fb_helper_fb_release(struct fb_info *info, int user);
> +
>  void drm_fb_helper_set_suspend(struct drm_fb_helper *fb_helper, bool suspend);
>  void drm_fb_helper_set_suspend_unlocked(struct drm_fb_helper *fb_helper,
>  					bool suspend);
> @@ -473,6 +476,16 @@ static inline void drm_fb_helper_cfb_imageblit(struct fb_info *info,
>  {
>  }
>  
> +static inline int drm_fb_helper_fb_open(struct fb_info *info, int user)
> +{
> +	return -ENODEV;
> +}
> +
> +static inline int drm_fb_helper_fb_release(struct fb_info *info, int user)
> +{
> +	return -ENODEV;
> +}
> +
>  static inline void drm_fb_helper_set_suspend(struct drm_fb_helper *fb_helper,
>  					     bool suspend)
>  {
> -- 
> 2.14.2
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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